Elastic fiber finds broad application as an industrial material and stretchable fabric material, which, due to its excellent stretch characteristics, is used in leg wear, inner wear, sportswear, etc.
High strength stretch, high resilience, high chemical resistance, high heat resistance and dye colorfastness are required of such elastic fibers, especially polyurethane elastic yarns. In particular, in the area of chemical resistance, fabric blends using combinations with polyester yarn have seen strong demand, and processing such polyesters to make them lighter in weight and stain resistant requires resistance to chemicals such as alkalis, quaternary ammonium salts, unsaturated fatty acids, etc.
Conventional technology that has been used to impart such chemical resistance involves including polyvinylidine fluoride in the polyurethane spinning solution. See Japanese Patent No. Sho 60-44406.
However, such polyurethane elastic yarn which includes polyvinylidine fluoride exhibits inadequate resilience and heat resistance, and especially, when used in blended fabrics with polyester yarn that undergo weight reduction or stain proofing processing, the chemical resistance of the resulting fabric is insufficient, which can limit its use.
Other such technology involves including modified polyvinyl alcohol sulfonate or synthetic tannins of sulfone compounds in the polyurethane spinning solution. See U.S. Pat. No. 6,635,347 and Japanese Patent No. Hei 7-68657. However, even when compounds containing sulfonate groups are included, their low content ratio also causes unsatisfactory levels of chemical resistance, especially in polyester blended fabrics that require stain proofing processing. Further, in the case of the latter, the compounds themselves exhibit a dark brown color, which strongly adheres to the resulting yarn, thereby limiting its use.
Furthermore, polyurethane elastic yarn is made from a wide variety of raw materials, and it is used in an increasingly broad range of blends, not just with synthetic fibers such as nylon or polyester, but also with natural fibers such as cotton, wool, and semi-synthetic fibers. Accordingly, when stretchable products are dyed, good colorfastness may also be required depending upon the application.
In conventional stretchable products, each of the raw materials is dyed independently which leads to good colorfastness, but since such good colorfastness cannot be achieved in polyurethane fibers, they are usually left undyed. The reasons for this lie in the chemical structure, in that the polyurethane polymer does not have sufficient functional groups for dye adsorption, and further, due to its low degree of crystallization, once dyed, it cannot retain the dye in a colorfast manner. Accordingly, in fabrics containing polyurethane elastic yarn, the only way to achieve a practical degree of colorfastness is through the repeated washing of the fabric to remove the dye that has not been chemically adsorbed. However, not only does the repeated washing out of dye that was initially adsorbed into the fabric entail the wasteful use of large quantities of water and energy, but it results in poor color reproducibility among different dyed lots.
However, if the polyurethane elastic yarn left undyed, when the fabric is stretched, the internal polyurethane elastic yarn is brought to the surface, which detracts from the aesthetics and the color depth of the fabric, thereby leaving a demand for combinations of fiber raw materials that can be dyed to the same color, and this demand is especially strong for dark colors such as black used in fiber products. Furthermore, an additional demand exists for ways to change the color of fiber products, such as to dye the raw materials in blends using polyurethane elastic yarn to different colors.
One technology known to the prior art for dyeing elastic fibers involves adding pigments to the polyurethane spinning solution to produce spun-dyed yarn. See Japanese Unexamined Patent Application No. 2000-73233. Although such polyurethane elastic yarn containing pigments exhibits excellent colorfastness, the number of colors that can be used is limited and very costly, which limits its applications.
Another conventional dyeing technology involves the addition of an amine to elastic yarns such as polyurethane, and using the adsorption of acidic dyes or metal-containing dyes. However, in cases where their terminal group radical weight is low, adequate color density cannot be achieved, and conversely, when the amine terminal group radical weight is increased, due to the differing dye adsorption properties with the other fibers such as nylon that are in the blend, when dyeing with formulations of the three primary colors, different colors are produced, which makes color matching very difficult.
Yet another conventional dyeing technology involves the use of dye dispersions. Although the dispersed dyes produce good absorption in the polyurethane elastic yarn, the adsorptive strength of the dye remains weak, and it is impossible to obtain highly dense colors, or for the mid-density colors to remain colorfast during use. See Japanese Patent No. 3826377.
Further, another fiber structure involves the use of polyether-polyester block copolymer elastic fiber, which can be dyed with cationic dyes. However, because polyether-polyester block copolymer elastic fiber has a lower degree of elongation and inferior heat resistance compared with polyurethane elastic fiber, it is only rarely used. Japanese Unexamined Patent Application No. 2001-140167.